The invention relates generally to a method and system for evaluating chemical deterioration of oil used in automotive internal combustion engines. More specifically, the invention relates to a method and system for evaluating oil deterioration over time based on a change in the quantity of the vehicle""s oil.
It is well-known that an important aspect of automotive vehicle maintenance includes maintaining good engine lubrication. Because the chemical quality of automotive oil responsible for maintaining good engine lubrication deteriorates over time, good maintenance practices require that the vehicle""s oil be changed periodically. Many modern automotive vehicles include among their instrument clusters oil change indicators that notify vehicle operators when it is recommended that the vehicle oil be changed. These vehicles generally include electronic controllers that selectively activate the oil change indicator when it is determined that the vehicle""s oil should be changed. Various methods have been used to determine when and under what conditions a vehicle""s electronic controller activates the oil change indicator.
One known method is for the controller to activate the oil change indicator when the number of miles that the vehicle has traveled since the last oil change exceeds a certain pre-determined maximum recommended number of miles. For example, the controller might activate the oil change indicator every time the vehicle travels more than 5,000 miles since the previous oil change. Essentially, this method assumes that a vehicle""s oil, regardless of the quality of the oil used or the conditions under which the vehicle is operated, deteriorates to an impermissibly low level after such fixed number of miles. Because this method does not consider the quality of the oil used or the vehicle""s operating conditions, this method many times results in the oil change indicator being activated even though the vehicle""s oil still has remaining useful life.
Another known, and more sophisticated, method involves attempting to directly evaluate the deterioration of the vehicle""s oil over time by sensing and measuring a change in electrical conductivity of the vehicle oil over time. Because the conductivity of oil decreases as the chemical qualities of the oil deteriorate, the controller activates the change oil indicator when it determines that the oil""s conductivity has fallen to a level that corresponds to an impermissible deterioration of the oil quality. This method is limited in its usefulness at least because (i) the conductivity sensor cannot detect the initial quality of different types of oil; (ii) oil that is added between complete oil changes must be of the same initial quality as the original oil; and (iii) excessive data xe2x80x9cnoisexe2x80x9d in sensing the electrical conductivity makes the method relatively inaccurate. With respect to the data xe2x80x9cnoisexe2x80x9d limitation, it is known that the occurrence of water condensation in the oil changes the overall conductivity of the oil significantly, which leads to inaccurate conclusions regarding the quality of the oil. Accordingly, this method has not been effectively used in production.
Yet another known method involves indirectly estimating the deterioration of the vehicle oil over time based on a variety of vehicle operating data, such as total engine RPMs, total number of cold starts, time interval since previous oil change, etc. Recognizing that different driving conditions result in the deterioration of oil quality at different rates, this method applies complex models and algorithms to the measured vehicle operating data to estimate the rate of oil quality deterioration. This method is limited at least because it requires that several operational data be sensed and stored in system memory, and the algorithms for estimating the oil degradation are complex.
Accordingly, there is a need for a simpler and more accurate system and method for evaluating the quality of a vehicle""s oil.
The present invention generally relates to a new method to evaluate the quality of a vehicle""s oil that is both more accurate and more efficient to implement than existing methods and systems. Based on the oil quality evaluation, the vehicle""s electronic controller selectively activates either an xe2x80x9coil changexe2x80x9d indicator or a xe2x80x9clow oilxe2x80x9d indicator in the vehicle""s instrument cluster to provide appropriate maintenance information to the vehicle operator.
The inventor hereof has discovered that oil consumption in an internal combustion engine increases significantly after the chemical quality of the oil deteriorates past a certain point. As a result, when the oil quality sufficiently deteriorates, the quantity of the oil in the system falls significantly. FIG. 1A generally illustrates the inventor""s empirical observation that oil quantity in an internal combustion engine generally decreases over time as a result of operation. FIG. 1B generally illustrates the inventor""s empirical observation that oil quality (measured in terms of Total Base Number (TBN)) tends to deteriorate over time as a result of operation. The inventor has discovered that a useful correlation exists between the amount of oil consumption and the quality of the remaining oil in the system. Specifically, oil is consumed by the engine much more rapidly once the oil""s quality deteriorates past a certain point. The present invention uses the correlation between oil consumption (loss of oil quantity) and oil quality deterioration to evaluate the chemical quality of a vehicle""s oil over time and to signal the vehicle operator as to when it is appropriate to either add oil or completely change the vehicle""s oil.
An oil quantity sensor, preferably positioned in the vehicle""s oil pan, detects the oil quantity in the vehicle""s oil system. When the oil quantity sensor detects that the oil level in the oil system has fallen to a certain low oil reference value, the controller selectively activates either a xe2x80x9cchange oilxe2x80x9d indicator or xe2x80x9clow oilxe2x80x9d indicator based on the change in oil quantity and certain oil maintenance parameters indicative of the driving conditions under which the vehicle has been operated.